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PVC integrity?

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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PVC integrity?

Unread postAuthor: Pyro451 » Sun Nov 27, 2011 9:39 pm

First of all, I'd like to say hi, as this is my first post in this forum.


Now, down to the topic of this post: What is the pressure limit of 3" PVC pipe? We're using a pressure plate/combustion chamber design my friend came up with (We're both high school juniors who participate in a few engineering and robotics clubs/classes/competitions). The point being that the entire gun is made of one 7' piece of 3" PVC pipe with a piece of machined metal plate about 18" from the end with a 1/4" hole that provides pressure.

So, seeing as how PVC, when over pressured, has a tendency to fragment into large, sharp pieces, and that this gun is shoulder-mounted, what propellants can I feel adequately safe about using? Right now, we're using chocolate Axe, which works well (minus the noxious fumes) and has a tendency to make the gun smell awesome, but I'm thinking of switching over to nitromethane RC fuel. Would that make the gun likely to explode?


Also, there is the matter of the projectile; currently, were using empty water bottles wrapped with duct tape and paper towel to a tight fit. They go a good 100 feet or so on a full shot. (We shot it into a wooden fence today from ten feet away. The cap was found inside the bottle.)

I have an idea for another projectile- a 6" section of 2.5" pipe with endcaps, filled with wet newspaper, with some sort of machined nose cone on the front. What weight should I go for?
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Unread postAuthor: warhead052 » Sun Nov 27, 2011 9:48 pm

From what I have heard, and average combustion only generates about 50 psi, so I would say your safe. So pvc should hold up.
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Re: PVC integrity?

Unread postAuthor: jackssmirkingrevenge » Sun Nov 27, 2011 10:12 pm

Pyro451 wrote:I'm thinking of switching over to nitromethane RC fuel. Would that make the gun likely to explode?


You're better off metering butane/propane/MAPP than píssing about with liquid fuel ;)

I have an idea for another projectile- a 6" section of 2.5" pipe with endcaps, filled with wet newspaper, with some sort of machined nose cone on the front. What weight should I go for?


That will just tumble end over end, you're better off capping just one end and pouring something heavy for 25% of the pipe length.
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Unread postAuthor: Pyro451 » Sun Nov 27, 2011 10:16 pm

From what I have heard, and average combustion only generates about 50 psi, so I would say your safe. So pvc should hold up.


All right, thanks. The reason I'm concerned about this is because I used to be into home made fireworks (rockets, mortars, etc.). And the #1 rule of making mortars is to never use PVC in any part of your launching setup because if there is a jam/the powder load is too high, it turns into a grenade.

You're better off metering butane/propane/MAPP than píssing about with liquid fuel


MAPP gas? Pretty nasty stuff, but if it works, it shouldn't be too hard to adapt the gun to use that- we're already using a ball valve to inject/seal the chamber.
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Last edited by Pyro451 on Sun Nov 27, 2011 10:26 pm, edited 1 time in total.

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Unread postAuthor: warhead052 » Sun Nov 27, 2011 10:22 pm

Yeah, I understand the fireworks. But that sort of discussion isn't really allowed here. But I do understand your wariness. Glad to see a new member who is concerned about safety.

Be sure to post pictures of the cannon when its done!
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 27, 2011 10:28 pm

Pyro451 wrote:MAPP gas? Pretty nasty stuff, but if it works, it shouldn't be too hard to adapt the gun to use that- we're already using a ball valve to inject/seal the chamber.


No need to make any changes to the launcher,here you go.
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Unread postAuthor: Pyro451 » Sun Nov 27, 2011 10:33 pm

Be sure to post pictures of the cannon when its done!


Will do. We have big plans for this thing, and, knowing us, we'll probably get bored really fast and escalate until either it breaks or we have something that doesnt resemble anything we started with.

Yeah, I understand the fireworks. But that sort of discussion isn't really allowed here. But I do understand your wariness. Glad to see a new member who is concerned about safety.


Thanks.

That will just tumble end over end, you're better off capping just one end and pouring something heavy for 25% of the pipe length.


I'll try that. We're probably gonna spend an afternoon launching various projectiles while laughing maniacally- you know, to see which design works best.
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Unread postAuthor: Zeus » Sun Nov 27, 2011 10:41 pm

Pyro, I can't help with your question, but I see you know the flash point of paper.

There's a few here with such interests, just don't mention in on this forum.
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Unread postAuthor: Pyro451 » Sun Nov 27, 2011 10:48 pm

Pyro451 wrote:
Be sure to post pictures of the cannon when its done!


Will do. We have big plans for this thing, and, knowing us, we'll probably get bored really fast and escalate until either it breaks or we have something that doesnt resemble anything we started with.

Yeah, I understand the fireworks. But that sort of discussion isn't really allowed here. But I do understand your wariness. Glad to see a new member who is concerned about safety.


Thanks.

That will just tumble end over end, you're better off capping just one end and pouring something heavy for 25% of the pipe length.


I'll try that. We're probably gonna spend an afternoon launching various projectiles while laughing maniacally- you know, to see which design works best.

No need to make any changes to the launcher, here you go.


Thanks. I saw the 3% butane/ideal air ratio thingy and thought it looked off, so I spent the last 5 minutes calculating that (AP Chem FTW). Came out with 3.2% exactly. I will never doubt you again.
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Unread postAuthor: Pyro451 » Sun Nov 27, 2011 10:55 pm

Pyro, I can't help with your question, but I see you know the flash point of paper.

There's a few here with such interests, just don't mention in on this forum.


Yeah, I kinda figured out from lurking around that, as a general rule, on these forums, fire outside of the cannon=bad.

And the name is less about my propensity for being a pyro and the flash point of paper, and more about my love of Fahrenheit 451 and the fact that it's sort of a universal handle for me across a dozen or so sites on the internet. Although, currently, there is a sort of shadow war between me and some neckbearded fellow in Canada for that name, leading to half the sites I register for denying my name because that guy already took it.
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Re: PVC integrity?

Unread postAuthor: velocity3x » Sun Nov 27, 2011 10:55 pm

Pyro451 wrote:What is the pressure limit of 3" PVC pipe?


3" sch 40= Working Pressure 260 psi
3" Sch 80= Working Pressure 370 psi

http://www.harvel.com/tech-specs-pvc-pipe-80.asp
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Unread postAuthor: Pyro451 » Sun Nov 27, 2011 11:07 pm

Alright, thanks, Velocity. Now I don't have to worry about this thing blowing up in my face.
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Unread postAuthor: EpicMadness » Mon Nov 28, 2011 4:00 am

on my area common PVCs are always unrated and unspecified, inshort you gamble on what you get, its just a plastic unmarked pipes BUT there are rated pipes here and there, well the unrated pipes are like 1/3 of the price of the rated ones so you know :oops:

well the reason why they dont bother rating them is that most of the pipes ends up being used as a storm drain pipe which hardly needs pressure ratings. plus i got a theory that those unrated pipes are pipes that failed their tests and so on.


what i do to test their strength and so on is cut 2inch long sections and put one in a freezer and the other slightly heated(boil it in water), and do my unreliable tests like use a hammer to strike and try to shatter them. some doesn't shatter and some are freaking brittle like crackers.
since i only took a fraction of the whole pipe, what i do with the rest are that the useless ones ends up as what they're meant to be used for, storm drain pipes, the great and durable ones are then subjected to [s]inhumane[/s] torture like using them as an air tank or a barrel, i use rated ones for the chamber or find an extra thick unrated one that seems to work wonders for me.
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 28, 2011 4:43 am

Still waiting for someone to take up this challenge...
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Unread postAuthor: EpicMadness » Mon Nov 28, 2011 5:01 am

jackssmirkingrevenge wrote:Still waiting for someone to take up this challenge...


jesus crist, i think you just made me comment on a dead thread...
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